Roundtrip serialization of coordinate variables with spaces in their names

[shoyer]

If coordinates have spaces in their names, they get restored from netCDF files as data variables instead:

>>> xarray.open_dataset(xarray.Dataset(coords={'name with spaces': 1}).to_netcdf())
<xarray.Dataset>
Dimensions:           ()
Data variables:
    name with spaces  int32 1

This happens because the CF convention is to indicate coordinates as a space separated string, e.g., coordinates='latitude longitude'.

Even though these aren't CF compliant variable names (which cannot have strings) It would be nice to have an ad-hoc convention for xarray that allows us to serialize/deserialize coordinates in all/most cases. Maybe we could use escape characters for spaces (e.g., coordinates='name\ with\ spaces') or quote names if they have spaces (e.g., coordinates='"name\ with\ spaces"'?

At the very least, we should issue a warning in these cases.

[fmaussion]

I would be in favour of issuing a warning only and discourage using spaces in variable names altogether.

[shoyer]

I would be in favour of issuing a warning only and discourage using spaces in variable names altogether.

Even if we eventually implement this in some form, adding the warning would certainly be a good place to start.

[stale]

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If this issue remains relevant, please comment here or remove the stale label; otherwise it will be marked as closed automatically

[crusaderky]

Still valid in xarray 0.13, netcdf4-1.4.3.2

[kmuehlbauer]

Current state of affairs:

xr.open_dataset(xr.Dataset(coords={'name with spaces': 1}).to_netcdf())

SerializationWarning: coordinate 'name with spaces' has a space in its name, which means it cannot be marked as a coordinate on disk and will be saved as a data variable instead
  xr.open_dataset(xr.Dataset(coords={'name with spaces': 1}).to_netcdf())

Shall we close here or are there any actions which should be taken?

[kmuehlbauer]

Please reopen, if still relevant.